MicroRNAs (miRNA) are a recently discovered class of small non-coding RNAs (17-14 nucleotides). Due to their function as regulators of gene expression they play a critical role both in physiological and in pathological processes, such as cancer (Calin and Croce 2006; Esquela-Kerscher and Slack 2006; Zhang, Pan et al. 2007; Sassen, Miska et al. 2008).
There is increasing evidence that miRNAs are not only found in tissues but also in human blood both as free circulating nucleic acids (also called circulating miRNAs) and in mononuclear cells. A recent proof-of-principle study demonstrated miRNA expression pattern in pooled blood sera and pooled blood cells, both in healthy individuals and in cancer patients including patients with lung cancer (Chen, Ba et al. 2008). In addition, a remarkable stability of miRNAs in human sera was recently demonstrated (Chen, Ba et al. 2008; Gilad, Meiri et al. 2008). These findings make miRNA a potential tool for diagnostics for various types of diseases based on blood analysis.
Lung cancer is the leading cause of cancer death worldwide (Jemal, Siegel et al. 2008). Its five-year survival rate is among the lowest of all cancer types and is markedly correlated to the stage at the time of diagnosis (Scott, Howington et al. 2007). Using currently existing techniques, more than two-thirds of lung cancers are diagnosed at late stages, when the relative survival rate is low (Henschke and Yankelevitz 2008). This reality calls for the search of new biomarkers that are able to catch lung cancer while it is still small and locally defined.
Various markers have been proposed to indicate specific types of disorders and in particular cancer. However, there is still a need for more efficient and effective methods and compositions for the diagnosis of diseases and in particular cancer.